EP0135738A1 - Read write magnetic head for vertically magnetizable recording medium - Google Patents

Abstract

A magnetic write/read head for a recording medium to be magnetized perpendicularly is disclosed. The head contains a conduction body for carrying the lines of magnetic flux, two pole legs which are arranged adjacent the other in the direction of relative motion of the head and medium and having a predetermined distance from each other. At least one coil winding is associated with the two pole legs. The magnetic head is of a mechanical design which ensures a switchable write and read function with high efficiency. One of the two pole legs has a region of reduced cross section. A separate coil winding is associated with each pole leg and, for performing the write function, this region can be driven into magnetic saturation by means of a coil winding which is associated with the pole leg having the region of reduced cross section. Additionally, one of the two pole legs may include a region of magnetizable material having a predetermined Curie temperature which can be heated during the write function above the Curie temperature.

Description

The invention relates to a read / write magnetic head for a recording medium which is provided with at least one magnetizable storage layer which contains a magnetically anisotropic material whose axis of easy magnetization is oriented substantially perpendicular to the surface of the medium, and into the longitudinal information is to be written into a track by vertical magnetization of the storage layer, which magnetic head has a guide body guiding the magnetic flux with two pole legs, which are arranged one behind the other in the direction of movement of the head and at a predetermined distance from one another and to which at least one coil winding is assigned, the reading function being assigned to the Flow guide directions in the two pole legs at least largely run antiparallel at their ends facing the recording medium. Such a magnetic head emerges from DE-OS 29 24 013.

The principle of vertical magnetization for the storage of information is generally known (cf. for example "IEEE Transactions on Magnetics", vol. MAG-16, no. 1, Jan. 1980, pages 71 to 76 or the aforementioned DE-OS). This principle, which is also often referred to as vertical magnetization, requires special recording media, for example in the form of a rigid magnetic storage disk, a flexible single disk (floppy disc) or a magnetic tape. A corresponding recording medium has at least one magnetizable memory layer of a predetermined thickness, which contains a magnetically anisotropic material, in particular made of a CoCr alloy, the axis of which is slightly magnetized and perpendicular to the surface of the medium. Using a special write head, the individual information is then written along a track in successive sections, also called cells or blocks, by magnetizing the storage layer. In practice, the magnetic flux changes, ie the transitions from one magnetization direction to the opposite, are generally used as information. The sections have a predetermined extent, also referred to as the wavelength, in the longitudinal direction of the track. This expansion can be significantly smaller than the limit given in the longitudinal storage method by demagnetization, so that the information density in the recording medium can advantageously be increased according to the principle of perpendicular magnetization.

With this principle of vertical magnetization, however, problems arise in the development of corresponding combined read / write heads. With these heads, the desired flow guidance to a closed circuit with low magnetic resistance is particularly difficult.

A suitable combined read / write head, ie a magnetic head, with which both the write and the read function is to be carried out, generally has a so-called main pole, with which a sufficiently strong vertical magnetic field for reversing the magnetism of the individual sections in the storage layer is produced. The necessary conclusion can then be made, for example, by means of a so-called auxiliary pole on the opposite side of the recording medium (cf. the literature reference mentioned "IEEE Trans. Magn.", Vol. MAG-16). In addition, the inference from the leakage flux is also known ("IEEE Trans. Magn.", Vol. MAG-18, no. 6, Nov. 1982, pages 1170 to 1172).

Furthermore, a conclusion can also be made with a special auxiliary pole, which is located on the same side as the main pole (cf. "IEEE Trans. Magn.", Vol. MAG-17, no. 6, Nov. 1981, pages 3120 to 3122 or vol. MAG-18, no. 6, Nov. 1982, pages 1158 to 1163 or the aforementioned DE-OS 29 24 013). Accordingly, the read and write magnetic head known from DE-OS 29 24 013 contains, in the direction of movement of the recording medium moved beneath it, an auxiliary pole on its front end and the actual main pole on its rear side. This main pole is formed by a pole leg, which essentially consists of a thin pole piece running perpendicular to the direction of movement, which is applied to a non-magnetic substrate. The auxiliary pole, which is more extensive in the direction of movement and which lies in front of the main pole, is formed by a pole leg which is composed of a plurality of thin pole pieces arranged perpendicular to the direction of movement with insulating layers in between and which is separated from the main pole by an air gap. The expansion of this air gap is relatively large and is, for example, in the order of 5 to 10 _/ um. In the air gap there is an electrical winding with which the main pole can be excited for the writing function or the excitation of the main pole can be registered for the reading function. The auxiliary pole serves in any case only for the return of the river. A possible recording of the auxiliary pole can be accepted, since the main pole always lags behind it and thus overwrites any information written by the auxiliary pole, provided the width of the auxiliary pols is not greater than that of the main pole and thus neighboring tracks already described remain unaffected. In addition, the larger cross section of the auxiliary pole compared to the main pole and the relatively large expansion of the air gap are required to ensure a substantial reduction in the magnetic flux density at the auxiliary pole. However, reading the auxiliary pole can lead to difficulties in information recognition.

The residual space of the air gap which is not filled by the electrical winding and faces the recording medium must be filled with a so-called insulating gap layer. This gap layer should consist of the hardest possible material, such as A1 ₂ 0 ₃ , in order to avoid indentations or washouts during the manufacture of the head. Such bumps can lead to the crash of the magnetic head, which is guided over the recording medium at an extremely short distance, by dirt particles that are embedded. However, it has been shown that the production of this gap layer lying between the main and the auxiliary pole is extremely difficult to carry out.

Due to the difficulties mentioned when reading with the known combined read and write head, the function of writing and reading can also be carried out with separate heads, so that these heads can be optimally adapted to the respective function (see, for example, "IEEE Trans "Magn.", Vol. MAG-16, no. 5, Sept. 1980, pages 967 to 972). Known ring heads can be used for reading, while writing can be carried out with special heads. A write head suitable for this purpose has, for example on its side facing the storage layer of the recording medium, a main pole with a longitudinal extension, also referred to as a single-pole head voltage of, for example, 3 _/ um, on the opposite side of which is a much more extensive auxiliary pole. The second, only required to read head is a known ring head and has a gap width of, for example, 0.2 _/ um (see. "IEEE Trans. Magn.", Vol. MAG-17, no. 6, November 1981, pages 2538 to 2540). Corresponding devices for reading and writing with special heads adapted to the respective function are structurally relatively complex.

It is therefore an object of the present invention to improve the above-mentioned read / write magnetic head in such a way that, on the one hand, the problems mentioned with such combined heads are reduced in terms of their mechanical structure and, on the other hand, a switchable write and read function with high efficiency in each case is guaranteed.

This object is achieved according to the invention in that one of the two pole legs has a region with a reduced cross section, that each pole leg is assigned its own coil winding, and that for the write function, by means of the coil winding which is associated with the pole leg with the ^/ cross section reduced region, this area reduced in cross section is driven into magnetic saturation.

The advantages associated with this configuration of the magnetic head can be seen in particular in the fact that the region of the one pole leg that is driven into saturation for the write function acts as a barrier to the magnetic flux in this leg, so that this pole leg practically does not participate in the write function. With the other pole leg, the magnetic head thus quasi-writes the information into the recording medium as a single-pole head. Because flow changes when reading are significantly smaller than when writing, there is no danger that the pole leg with the area with reduced cross section will become magnetically saturated at this point. The magnetic head can thus be operated as a ring head for the reading function in a known manner. For this reason, the distance between the pole leg ends can also advantageously be kept very small, so that the head has correspondingly good reading properties. In addition, the risk of washing out the gap formed between these ends is at least largely excluded.

A further solution to the mentioned object is according to the invention is that one having the P _o lschenkel a portion of a magnetizable material having a predetermined Curie temperature and that means are provided, around this area to heat during the write function above the Curie temperature. As a result, the pole piece becomes paramagnetic in this area, ie the permeability then becomes approximately 1, so that this area acts practically like an air gap with a correspondingly high magnetic resistance for the flux in the pole piece. In this way, a magnetic field with a very pronounced vertical component, which is used to write the information into the recording medium, can advantageously be concentrated on the other pole leg.

Advantageous embodiments of the magnetic heads according to the invention emerge from the subclaims.

To further explain the invention, reference is made to the schematic drawing, in which Fig. 1, a magnetic head is illustrated. 2 shows a diagram with a magnetization curve for this magnetic head. FIGS. 3 and 4 each show a further embodiment of a magnetic head according to the invention posed.

In the read / write magnetic head according to the invention shown as a longitudinal section in FIG. 1, a known head is assumed, as can be seen, for example, from DE-OS 29 24 013 mentioned at the beginning. The head, generally designated 2 in the figure, which is shown during its writing function according to the principle of vertical (vertical) magnetization, is located on the front or rear side of a common component which is referred to as a missile and which is not shown in more detail in the figure . It is to be guided relative to a recording medium 2 known _per se at a low flying height f of, for example, 0.2 μm _, over this medium. For example, the recording medium is passed under the magnetic head. The relative direction of movement of the magnetic head 2 with respect to the recording medium 2 is indicated by an arrowed line denoted by v.

The recording medium 3, e.g. a magnetic storage disk, has a storage layer 4, in particular made of a CoCr alloy, which has a predetermined thickness d. This layer can optionally be coated on its side facing away from the magnetic head 2 with a soft magnetic layer 5, e.g. made of a special NiFe alloy. The storage layer 4 and optionally the layer 5 are deposited on the upper flat side of a carrier body 6 of the recording medium 3.

The magnetic head 2 has two pole legs 7 and 8, which are largely aligned, in particular at their ends 9 and 10 facing the recording medium 3, at least approximately perpendicular to the surface of the recording medium 3. Between these pole leg ends there is an air gap 11 with an advantageously small longitudinal, ie width w pointing in the direction of movement, less than 1 _/ um, in particular formed below 0.3 _/ um. In a central zone 12, the distance between the two pole legs 7 and 8 is widened with respect to the gap width w, for example in that the pole leg 7, which is rearward with respect to the direction of movement, leads in this zone to a greater distance w 'with respect to the front pole leg 8 which is just formed. Because of the space 13 formed in this way between the legs 7 and 8, it is possible for at least parts of each pole leg to be surrounded by its own coil winding 14 or 15 in this zone 12. Outside this zone on the side facing away from the recording medium 3, the pole legs are brought together again in a known manner.

According to the invention, one of the two pole legs, for example the pole leg 8, has a narrowed region 17, the cross section of which is considerably smaller, in particular at least three times smaller than the cross section of the other parts of this pole leg. The coil winding 15 is assigned to this area 17. With this winding, a sufficiently large, constant magnetic field can be generated in order to drive the material of the pole leg 8 into the magnetic saturation in this region (cf. FIG. 2). This area 17 then acts as a magnetic barrier for the magnetic flux which is generated by the coil winding 14 assigned to the other pole leg 7 and which is indicated by an arrowed line 18. At the end 10 of the pole leg 8 with the narrowed area 17 there is thus at most a minimal magnetic flux indicated by an arrowed line 19, so that the write function is practiced only with the magnetic flux 18 of the other pole leg 7. The resulting magnetization of a section 20 in the storage layer 4 is illustrated by an arrowed line 21. In the figure, the longitudinal extent 1 of this storage section 20 is in size order of the corresponding distance between the outer edges of the pole leg ends 9 and 10 shown. In general, however, this extent 1 is smaller, so that with the magnetic head 2 according to the invention a higher information density in the recording medium 3 is achieved than the geometric extent of the two pole legs would correspond (cf. for example also "IEEE Trans.Magn.", Vol MAG-17, no. 6, Nov. 81, pages 2538 to 2540).

For the reading function, both coil windings 14 and 15 can be connected in series so as to increase the signal voltage caused. An undesired saturation in the narrowed area 17 is not to be feared here.

In the manufacture of the magnetic head 2 using thin-film technology, a substrate 23 is generally used, which consists, for example, of TiC and Al ₂ O ₃ . If necessary, the substrate 23 can be provided with a sufficiently thick insulation layer, for example made of Al ₂ O ₃ . To build up the pole pieces 7 and 8, thin magnetic layers made of special NiFe alloys such as permalloy (Ni / Fe-81/19) or FeB are applied by sputtering, vapor deposition or galvanic deposition and by a non-magnetic intermediate layer made of e.g. Si0 ₂ or A1 ₂ 0 ₃ separated from each other. The magnetization of these magnetic layers lies in the layer plane. Due to the manufacturing process, the magnetic layers have a uniaxial anisotropy, that is to say that each magnetic layer has two anisotropy axes rotated by 90 °, which are referred to as the light or heavy direction. The magnetization is preferably parallel or antiparallel to the easy direction. The slight direction of the magnetic layers can be induced, for example, when the respective layer is applied by an applied magnetic field.

The grown, different layers are structured by techniques known per se, such as photolithography, plasma, ion beam or wet chemical etching, and thus the two pole legs 7 and 8 of the magnetic head 2 are produced. The easy direction of magnetization of the magnetic layers is generally always perpendicular to the direction of the magnetic flux in the pole legs, ie in the region of the ends 9 and 10 essentially parallel to the surface of the recording medium 3. After completion of one pole leg 8, an insulation layer, for example Si0 ₂ applied and then the coil windings 14 and 15 required for reading in and / or reading out the data in the magnetic storage layer 4 of the recording medium ₂ are produced or structured. These windings consist of Cu, Au or Al, for example. Since uneven magnetic layers cause their magnetic properties to deteriorate, the coil windings 14 and 15 can optionally be leveled in a known manner by means of polyimide lacquers. This is followed by the application and structuring of the second pole leg 7. Finally, a relatively thick protection layer, for example made of Al 2 O 3, is applied to protect the thin-film magnetic head 2.

With the magnetic head 2 shown in FIG. 1, a write function is currently to be performed. For this purpose, according to the invention, magnetization conditions are to be taken as a basis in the region 17 with a reduced cross section, as can be seen from the diagram in FIG. 2. In this figure, the magnetization M in the heavy direction as a function of the magnetic field strength H is shown as a curve. The following designations are selected here: M _s is the saturation magnetization, H ₀ is the field strength of the constant magnetic field which is generated with the coil 15, and Hk is the anistropy field strength of the material in the area 17 with reduced cross-section. H _↑ and H _↓ are the field strengths which result from the excitation of the coil winding 14 in this area 17 with reduced cross-section depending on the polarity direction.

It can be seen from the curve shown that the constant field H _O must be sufficiently large to achieve the saturation magnetization M _s in this region 17. In addition, the field H _{o is} to be chosen so large that the magnetic fields H ₀ , H _t and H _↓ occurring when writing to the area 17 are greater than the anisotropy field strength H _k , since both plus (↑) and minus (↓) Directions are written and H _↑ and H _{↓ are} each the result of the field H ₀ and the effect of the field caused in leg 7 on leg 8 (17).

A further embodiment of a magnetic head according to the invention can be seen from FIG. 3 in a representation corresponding to FIG. 1 during a reading function. Parts corresponding to FIG. 1 are provided with the same reference symbols. This magnetic head, designated 25, differs from the magnetic head 2 according to FIG. 1 essentially only by a simplified layer structure, in that a larger number of coil windings lying one above the other is avoided. Its longitudinal extent in the direction of flight is accordingly limited. For this purpose, its coil windings 28 and 29 assigned to the pole legs 26 and 27 each have two winding parts 30, 31 and 32, 33, which, according to the longitudinal section shown in the figure, are arranged one above the other perpendicular to the surface of the recording medium 3. In this case, only one partial winding 30 or 32 of the coil windings 28 and 29 is in the one formed between the pole legs 26 and 27 Intermediate space 35 housed, while the other partial windings on the upper side facing away from the recording medium 3, where the two pole legs 26 and 27 are re-assembled, are arranged on these pole legs. The partial windings 32 and 33 of the coil winding 29 are assigned to the reduced-section part 36 of the pole leg 27.

In the embodiments of the magnetic heads 2 and 25 according to FIGS. 1 and 3, it was assumed that the writing of one of the two pole legs is prevented by the fact that a region of reduced cross section is provided in this leg, which is driven into the saturation magnetization with the aid of a special coil winding . A further possibility for preventing an undesired writing of a pole leg can be seen from FIG. 4. The magnetic head shown in the figure as a longitudinal section and generally designated 40 corresponds in substantial parts to the magnetic head 2 according to FIG. 1. Corresponding parts are therefore provided with the same reference numerals. In order to prevent writing of the front pole leg 41 seen in the direction of movement with its end 10, this pole leg preferably has, according to the invention, at its end 10 facing the recording medium 3 a special area 42 which consists of a magnetizable material which has a predetermined Curie temperature T. _C. Corresponding materials are, for example, special FeNi alloys whose Curie temperature T _{C is} relatively low. For example, the alloy known under the trade name THERMOFLUX (registered trademark of Vacuumschmelze GmbH, Hanau) has a Ni content of about 30%, whereby a Curie temperature T _C between 30 ° and 120 ° C can be set by slightly varying the composition (cf. eg "Soft Magnetic Materials", publisher: Vacuumschmelze GmbH, Publisher: Siemens AG, Berlin and Munich, 3rd edition, 1977, especially pages 128 and 290 to 292). When writing, the area 42 made of such a material is then heated to such an extent that its temperature exceeds this Curie temperature T _C. As a result, the area 42 becomes paramagnetic, so that it practically represents an accordingly high resistance for the magnetic flux in the pole leg 41 like an air gap. In this way, only the rear pole leg 7, as seen in the direction of movement, which is correspondingly excited with the coil winding 14, writes. This coil winding can also be designed in accordance with the coil winding 28 according to FIG. 3.

The heating of the special area 42 above the Curie temperature T _C can take place, for example, through the write current of the coil winding 14. Of course, the area 42 can also be brought to the desired temperature by additional means for heating, not shown in the figure.

Due to the thin-film technology also to be used, the thermal capacity of the magnetic head 40 is so small that the heating of the head and in particular the area 42 of its pole leg 41 takes place sufficiently quickly. A rapid cooling during reading is advantageously promoted by a substrate 23, which consists of a good heat-conducting material. When cooling, the anisotropy direction of the magnetic layers of the region 42 is preferably set parallel to the magnetic layers of the region 42 by the stray fields of the magnetic layers of the pole leg 7 and by exchange coupling with the magnetic layers of the remaining part 43 of the pole leg 41, so that when reading the good properties of a longitudinal magnetic head can be achieved.

In order to determine whether the magnetic head 40 is ready to write, ie whether the Curie temperature T _{C has been} exceeded or whether it is ready to read, it is sufficient to carry out a measurement of the inductance of the coil winding 14 before writing or reading.

Claims (13)

1. Read / write magnetic head for a recording medium, which is provided with at least one magnetizable storage layer, which contains a magnetically anisotropic material, the axis of which is slightly magnetized, is oriented essentially perpendicular to the surface of the medium and into which information is provided along a track by vertical lines Magnetization of the storage layer are to be inscribed, which magnetic head has a guide body guiding the magnetic flux with two pole legs, which are arranged one behind the other and at a predetermined distance from one another in the direction of movement of the head and to which at least one coil winding is assigned, with the flow guide directions in the two pole legs for the reading function run at least largely antiparallel at their ends facing the recording medium, characterized in that one of the two pole legs (8, 27) has a region (17, 36) with a reduced cross section that each pole leg (7, 8; 26, 27) its own coil winding (14, 15; 28, 29) and that for the write function by means of the coil winding (15; 29), which is assigned to the pole leg (8, 27) with the area (17, 36) with reduced cross section, this area (17, 36) with reduced cross section 36) is driven into magnetic saturation. 2. Read / write magnetic head for a recording medium, which is provided with at least one magnetizable storage layer which contains a magnetically anisotropic material, the axis of which is slightly magnetized, is oriented essentially perpendicular to the surface of the medium, and into which information is passed along a track perpendicular magnetization of the storage layer are to be inscribed, which magnetic head blocks the magnetic flux has leading guide body with two pole legs, which are arranged one behind the other and at a predetermined distance from one another in the direction of movement of the head and to which at least one coil winding is assigned, the flow guide directions in the two pole legs at least largely antiparallel at their ends facing the recording medium for the reading function, thereby characterized in that one of the two pole legs (41) has a region (42) made of a magnetizable material with a predetermined Curie temperature and that means are provided to heat this region (42) above the Curie temperature during the writing function. 3. Magnetic head according to claim 1 or 2, characterized in that at least partially its magnetic flux leading parts (pole legs 7, 8, 26, 27, 41) consist of soft magnetic material. 4. Magnetic head according to one of claims 1 to 3, characterized in that its parts guiding the magnetic flux (pole legs 7, 8, 26, 27, 41) consist of a material whose slight magnetization is at least largely directed perpendicular to the direction of the magnetic flux. 5. Magnetic head according to claims 1 and 4, characterized in that for the write function with the coil winding (15, 29), which is assigned to the reduced cross-sectional area (17, 36); in this area (17, 36) caused constant magnetic field strength (H _O ) is greater than the anisotropy field strength (H _K ) of the material of this area (17, 36). 6. Magnetic head according to claim 5, characterized in that the magnetic field strength components (H,, H _t ), which in the pole leg (8, 27) with the reduced cross-sectional area (17, 36) due to the field with the constant magnetic field strength (H _O ) and caused by the excitation of the other pole leg (7, 26) in a parallel or antiparallel direction to the direction of the heavy magnetization of the material in this area (17, 36), always greater than the anisotropy field strength (H _K ) of the material this area (17, 36). 7. Magnetic head according to one of claims 1 to 6, characterized in that the distance (w) between the ends facing the recording medium (3) (9, 10) of the pole legs (7, 8, 26, 27, 41) under 1 / around lies. 8. Magnetic head according to one of claims 1 to 7, characterized in that between the pole legs (7, 8, 26, 27, 41) from the distance (w) between their the recording medium (3) facing ends (9, 10) a larger distance (w ') is formed in the intermediate space (13, 35) in which the coil windings (14, 15, 28, 29) are at least partially arranged. 9. Magnetic head according to claim 8, characterized in that each coil winding (28, 29) comprises two partial windings (30, 31 or 32, 33), one of the partial windings (30, 32) in the expanded space (35) and the other partial windings (31, 33) are arranged in an area in which the pole legs (26, 27) are brought together again on their side facing away from the recording medium (3) (FIG. 3). 10. Magnetic head according to one of claims 1 to 9, characterized in that at least partially its magnetic flux leading parts (pole legs 7, 8, 26, 27, 41) are applied as thin-film structures on a flat substrate body (23). 11. Magnetic head according to claim 10, characterized in that the coil windings (14, 15, 28, 29) are applied as thin-film structures on the substrate body (23) or on one of the pole legs (8, 27, 41). 12. Magnetic head according to claim 2, characterized in that the write current of the coil windings (14) is provided for heating the region (42) with the predetermined Curie temperature. 13. Magnetic head according to claim 2, characterized in that special means for heating the area (42) are provided with the predetermined Curie temperature.

Images